[Simh] pdp11 - console input with high bit set

[Paul Koning]

> On Jul 24, 2020, at 3:15 PM, Clem Cole <clemc at ccc.com> wrote:
> 
> 
> 
> On Fri, Jul 24, 2020 at 2:37 PM Paul Koning <paulkoning at comcast.net <mailto:paulkoning at comcast.net>> wrote:
> The right answer would be a tweak to the console emulation in SIMH pdp11.  
> Mumble... Paul - I'm not so sure.  While DEC used MARK a lot, there were places that used EVEN parity a lot also on PDP-11's (Lord how, I hated 20 mA current loop ;-) at least by the time of widespread RS-232C interfaces it was glass ttys and usually a full 8-bit data path.   7-bit with odd/even is defined this way:
> 
>  bits of data
> (count of 1-bits)	8 bits including parity
> even	odd
> 0000000	0	00000000	10000000
> 1010001	3	11010001	01010001
> 1101001	4	01101001	11101001
> 1111111	7	11111111	01111111
> FWIW:  I'm on a Mac and I run a program called 'Serial' that can do that; but  I thought most of the programs that simulate a serial connection for the different PC/Windows system have similar options.  Certainly that was true when I did it with DOS.

I use minicom, and yes, it can do all those things.  But that wasn't the case I was thinking about.  I thought the issue isn't so much the case where you have a terminal emulator program talking to a serial port, but rather the case of your command window in which you invoke simh (pdp11) and you're then talking to the console terminal.  I would rather not have to change the settings on my regular shell to deal with oddball stuff expected by some application, I figure that's the application's job.

> Anyway, I think the 'right' answer for simh is to ask the user to use a serial emulation program that can generate any of: 8-bit no parity, 7-bit no parity, or 7-bits of data plus an 8th parity bit with any of the 4 parity options:  odd, even, mark (aways 1) or space (always 0).   Seems to me, simh should bring 8 bits into the simulated serial port and let the SW running on the system decide what it's going to do with it.
> 
> I'm curious to hear what Bob thinks?  

Parity is something that comes in addition to the data.  DEC UARTS (and many others, I think) would let you set the data length (5, 6, 7, 8 bits) and the parity setting (none, even, odd).  So what you called "8 bits including parity" is technically "7 bits with parity".  If you set your UART for 8 bits with parity, it would send 11 bits total: start, 8 data, parity, stop.

I've even run into 10-bit UARTs (on PLATO terminals).  But that's not DEC stuff.

	paul

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